Quick release detent pawl



March 2l, 1950 l A, c, HOWARD 2,501,603

QUICK RELEASE DETENT 'PAWL Filed-1kb.l 2o, 1948- 2 sheets-sheet 1 I In luli I A I g l z I" i: 0 1l f i 59 i 36 L- i [619 I8 I f7 1- '.o. E Il2.- l5 3l I vl 3o 2a 5.21 372 53 I g 3,5I 37 26 l.

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l I A I l l In A en or 9m/ze 02051450 A Homey March 21, 1950 A A. c.HOWARD Quzcx- RELEASE DETENT PAwg.

2 Sheets-Sheet 2 Filed Feb. 20, 1948 MN wm Patented Mar. 21, 1950 U ,a

QUICK RELEASE DETENT PAWL Arthur Clifford Howard, Upminster, England,assignor of one-half to Rotary Hoes Limited, East Herndon, EnglandApplication February 20, 1948, Serial No. 9,727 In Great Britain June28, 1944 Section 1, Public Law 690, August 8, 1946 Patent expires June28, 1964 This invention relates to single and doubleacting lifting jacksof the pawl and rack operated type, whether reversible or otherwise.

These jacks, when single-acting, have an actuating pawl whereby the rackis raised step-bystep, and a detent pawl to hold the rack whilst theactuating pawl is moved in preparation for each lifting operation. Whenthese jacks are doubleacting, the actuating and detent pawls are eachadapted alternately to raise the rack and hold it. When the jacks arereversible, they can also be lowered step-by-step.

Lifting jacks of the type referred to have heretofore been provided withmeans for withdrawing the pawls from the loaded rack so as to drop theobject that had been lifted. In withdrawing the pawls, however, aprogressively diminish- -ing cross-section of the rack teeth isconstrained to withstand the full load, until disengagement iscompleted, with the result that the tips of the rack teeth, and in someinstances the pawls, have been damaged. Jacks that have sustained damageof this nature are rendered unreliable in action, due to faultyengagement of the pawls with the damaged rack teeth, and instances areknown where loads have inadvertently been dropped during normal liftingwith resultant injury to personnel and damage tothe object being lifted.

My object is to provide a jack, of the type set forth, with means forpermitting the lifting table to be lowered suddenly, While under load,without injury to the teeth of the rack or to the pawls.

According to the present invention, a jack of the type set forth isprovided with support means for the detent pawl, which support meanscan, ,when it is desired to drop the load and the actuating pawl iswithdrawn from the rack, be moved to un-support the detent pawl andpermit the latter to be urged freely out of engagement With the rack bythe descent of the latter due to the load.

An embodiment of the invention, as applied to 'a single-acting jack,will now be described with reference to the accompanying drawings, inwhich:

Figure l is a side elevation, partly in section, showing the variousparts in the positions they occupy at the completion of a liftingoperation; y Figure 2 is a fragmentary side elevation showing thelifting pawl retracted to permit the withdrawal of the detent pawl; and

Figure 3, which is a view similar to Figure 2,

s claims. (C1. zei- 108i Ate shows how the detent pawl is disengagedfrom the rack, so as to drop the load, Without the development of anyharmful pressure during such disengagement.

The jack shown comprises a body Il, a rack yI2 with a load-supportingtable I3 or I3'a, a lifting pawl I4, and a detent pawl I5.

The lifting pawl I4, as shown, is constructed and supported, asdescribed in British Patent No. 577,639, it being spring-loaded, asnecessary or desired, in any suitable manner. This comprises pivotallysecuring the foot of the pawl, by a strap I6, to a bearing barrel I1extending between the two side Walls of a hollow operating lever I8which latter is supported by external trunnions I9 in the jack body; thearrangement permitting the barrel Il and trunnions I9 to overlap forsecuring a high mechanical advantage and the barrel Il providing a largebearing surface for the pawl so as to secure a low intensity of loading.A tommy bar, not shown, is inserted in the lever I8 for operating thejack.

The detent pawl I5 is housed in a guide 20 which locates it laterallyand permits it to move obliquely into and out of engagement with therack. The foot of the detent pawl is pivoted at ZI in a cylindricalrecess at the top of a link 22 having its lower end similarly pivoted tothe arm 23 of a bell-crank lever 24 that is itself pivoted at 25 to thebody II; a spring-loaded hook member 2Ia holding the pawl and link inposition, and the bottom of the guide 20 forming a cross-head for thepivot 2 I. It will be seen that the link 22-and arm 23 form a toggle.The other arm 26 of the'bell-crank lever is substantially U-shaped incross-section and forms the bottom of a housing for-the reception of atommy bar 21. The top of this housing is constituted by the foot 28 of aslide 29 supported in a guide 30 formed in the body II; the top o theslide projecting through the guide at 3| just beneath the operatinglever I8.

During normal operation of the jack, that is,

with the parts as shown in Figure l, the foot of' the slide rests uponan arcuate portion 32 of one side Wall 33 of the U-section arms 26 ofthe bell-crank lever and engages behind an abutment 34 formed in thewall 33. The slide thus holds the bell-crank lever 26 with its pivot tothe link 22 in an overecentre position to the left of Figure 1 and withthe inner end abutting the guide 20 at 35. The thrust on the detent pawlis therefore supported by the pivot 25 of the bell-crank lever and atthe abutting point 35. In this position the operating lever I8 preventsthe slide 3 29 from being moved for disengaging its foot from theabutment 34, so that there is no fear of the support for the detent pawlbeing accidentally withdrawn.

When itis desired to drop the load, the operating lever I8 is raised tothe position shown in Figure 2, thus lowering the pawl I4, whichlatter', due to the co-action of its oblique surface 39 with thecross-bar 36 (which is fast with the body il), becomes disengaged fromthe rack; the load then being supported by the detent pawl. rIhismovement of the lever i3 removes its obstruction to the upward movementof the slide 29 so that, when the tommy bar 21 is inserted in the arm 26of the bell-crank lever to abut a stop 31, in which position it engagesthe underside of the foot 28 of the slide, the slide can be raised tofree the abutment 34. That is to say, depression of the free end of thetommy bar 2'1 causes the tommy bar to rook about the free end of the arm26 las a fulcrum, see Figure 3, and it during the nrst part of thismovement that the slide '29 is raised against the pressure of its returnspring 38, in order for its foot 28 teclear the abutment 34. As soon asthe abutment 34 has been cleared in this way the reaction of the tommybar on the free end of the arm 26 4causes the bell-crank lever 24 toturn clockwise with a action until its pivotal connection 'to the link22 passes over-centre with r-.espect to the pivots 2| and 2-5 so as toun-support the Idetent pawl i5. The rack then descends under the loadand traverses the detent along the guide v20.-; the `vinclination of thelatter to the line oi movement of the rack, and the 4spring-loading ofthe hook member 21a, -disengaging the pawl `from the rack. It will thusbe seen that, due to the detent pawl being 1in-supported duringdisengagement there is negligible pressure between it and the rack`teeth while the load is being dropped.

Also, as soon as the tommy bar has moved the 'bell-crank over thedead-centre position, during the disengagement of the detent pawl, thespring hook Zia asserts litself and enhances the .snap act-ion referredto above.

It will -be obvious that, inthe case vof a double- :acting jack, thedetent pawl can be supported in a manner similar to that abovedescribed.

Also, that the detent pawls of reversible jacks,

whether single vor double-acting may be similarly supported.

What `I `claim as my invention and desire to .secure by Letters Patentof the United States is: 1,. A lifting jack 'comprising a body, aratchettoothed rack fast with a table for supporting a -load AandaXialiy-slidably supported in said body, an 'operating lever pivoted tosaid body, a lifting pawl tor vcoacting with said rack .pivoted to said'operating lever, a detent pawl for coacting with said rack, a guide.for said detent pawl fast with said body and diverging .from vthe .axisci said rack, and movable means which in `one extreme position supportssaid detent `pawl for supporting said rack and which in an- ,otherposition, when said lifting pawl is withdrawn from engagement with saidrack, unsupfports said detent pawl so that the latter, due to theinclination of 'its said guide, -is urged out of engagement with `saidrack due to the descent of the flatter under the influence oi grav-ity.

2. :A lifting jack comprising a body, a ratchettoothed rack fast with atable `for .supporting a load and axially-slidably -supported in saidbody, an'operating vlever pivoted `to said body, a lifting pawl forcoaction with said rack pivoted to said operating lever, a detent pawlfor coaction with said rack, a guide for said detent paWl fast with saidbody and diverging from the axis of sa-id rack, movable means which inone extreme position supports said detent pawl for supporting said rackand which in another position. when said lifting pawl is withdrawn fromengagement with 'said rack, unsupports said detent pawl so that thelatter, due to the inclination of its said guide, 'is urged out ofengagement with said rack due to the descent .of the latter under theinfluence of gravity, and a locking-means for holding 'said movablemeans in the detent-pawl-support- Ving position, said operating leverobstructing the disengagement of said locking-means from said movablemeans except when said operating lever has been moved for completelywithdrawing said lifting pawl from engagement with said rack.

3. A lifting jack comprising a body, a ratchettoothed rack fast with aload-supporting table and laxially-slidably supported in said body, anoperating vlever pivoted to said body, a lifting -pawl for coaction withsaid rack pivoted to said operating lever, a toggle-means pivoted tosaid body, a detent pawl for coaction with said rack 4pivotallySupporta-ble by said toggle-means, locking-means for holding saidtoggle-means in an :angular position for supporting said detent pawl forfcoaction with rsaid rack, said operating lever obstructing thewithdrawalof said locking-means from the locking position except whensaid operating lever is swung to a non-operative position, a .lever fast-with said toggle means for coaction with a tommy bar ifor turning saidtoggle means, when unlocked, into lan angular position in which it-unsupports vsaid detent .pawL .said tommy -bar :reacting on saidlocking-means to move the latter :f-romits locking position, and aninclined guide for said detent pawl for withdrawing it, whenunsupported, from engagement with said rack by the .descent `of thelatter under gravity.

4. A lifting jack comprising a body, a ratchet- `toothed rack vfast witha load-supporting table and aXially-slidably supported in said body, anoperating ylever pivoted to said body, a lifting pawl Vfor coaction withsaid rack pivoted to said operating lever, toggle-means pivoted to saidbody, a detent pawl for coaction with said rack ,pivotally supportableby said toggle-means, a stop 'for holding said toggle-means in oneover-centre position "for supporting said detent pawl for coaction withsaid rack, locking-means for locking said toggle-means in said oneover-centre position, said operating lever obstructing the withdrawal ofsaid locking-means from the locking position except when said operatinglever is swung to-.a non-operative position, a lever fast with said,togglemeans for coaction with a tommy bar 'for vturning lsaid togglemeans, when unlocked, into an opposite `over-centre position in which itun- -supportssaid'detent pawl, said tommy bar reacting on vsaid lockingmeans to move the latter from its locking position, and a guide forzsaid "detent pawl extending obliquely-downwardly .from the fpathof therack, said guide being jfor withdrawing said detent pawl, when thelatter is unsupported, from engagement with said rack Yby lthedescent'ofthe latter under gravity.

V,5. Aflifting jack comprising a body, a ratchettoothed rack fast with aload-supporting table and aXially-slidably supported in said body, Aanoperating lever pivoted to said body, a lifting pawl for coactionwithsaid rack pivoted to said yoperating lever, .a 'bell crank leverpivoted to said body, a detent pawl, an inclined guide for Vsaid detentpawl for guiding it from engagement,

when unsupported, With said rack by the descent of the latter undergravity, a link connecting one arm of said bell-crank lever to the footof said detent pawl, an abutment fast with said body for holding saidbell-crank lever with said link in one over-centre position forsupporting said detent pawl for coaction with said rack, an abutmentformed on said bell-crank lever, and a slide guided by said body and forcoaction with said abutment on said bell-crank lever for locking saidbell-crank leverin the detent-paWl-supporting position, said operatinglever obstructing the withdrawal of said slide from the locking positionexcept when said operating lever is swungto a non-operative position inwhich said lifting pawl is disengaged fromsaid rack, the other arm ofsaid bell-crank lever being for coaction with a tommy bar for turningsaid bell-crank lever, when unlocked, to bring the connection betweensaid link and said one arm of said bell-crank lever into an oppositeover-centre position in which said detent pawl is unsupported, saidtommy bar reacting on said slide to move the latter from its lockingposition.

6. A lifting jack, according to claim 5, of which the said other arm ofsaid bell-crank lever is of channel section to form a lower housing partfor said tommy bar, and the adjacent end of said slide forms an upperhousing part for said tommy bar, the movement of said slide, whenunlocked, from its locking position being eected by pivoting the tommybar about the outer end pressure of said tommy bar on said outer endenabling said bell-crank lever being moved, with a snap action, forunsupporting said detent pawl.

'7. A lifting jack, according to cla-im 5, comprising a spring ,forbiassing said slide into its locking position.

8. A lifting jack comprising a body, a ratchettoothed rack fast with atable for supporting a load and axially-slidably supported in said body,an operating lever pivoted to said body, a lifting pawl for coactionwith said rack pivoted to said operating lever, a detent pawl forcoaction with said rack, a guide for said detent pawl fast with saidbody and diverging from the axis of said rack, movable means Which inone extreme position supports said detent pawl for supporting said rackand which in another position, when said lifting pawl is Withdrawn fromenga-gement with said rack, unsupports said detent pawl so that thelatter, due to the inclination of its said guide, is urged out ofengagement with said rack due to the descent of the latter under theinuence of gravity, and spring means acting on said detent pawl toassist in such disengagement of said detent pawl and rack.

ARTHUR CLIFFORD HOWARD.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 228,830 Morrison June 15, 1880359,405 Scott Mar. 15, 1887 1,391,594 Tatton Sept. 20, 1921

